Question

我有这个带有SwiftUI的程序。该程序用于基于3个用户输入的机器学习来计算就寝时间。我有一个Text（“”）向用户显示他们更新的就寝时间。

我希望程序自动更新就寝时间并将其显示在我的Text（“”）上。我尝试了很多方法，但似乎都没有用。到目前为止我尝试过的

onAppear-程序首次运行时就寝时间仅更新一次
onTapGesture-仅在点击选择器时更新就寝时间（滚动选择器不起作用），并且在某种程度上阻碍了更新步进器（单击+/-不会更改小时数）
将didSet与符合observableObject的类一起使用，在该类中使用@Pulished vars，在视图结构中使用@ObservedObject。效果不佳，但仅在类具有默认值时才尝试
在结构中使用didSet-它不会更新就寝时间

有人知道是否有一种更简便的方法来更新就寝时间，但是用户滚动选择器并在变量发生变化时进行滚动？

struct ContentView: View {

    static var defaultWakeUpTime : Date {
        var defaultTime = DateComponents()
        defaultTime.hour = 7
        defaultTime.minute = 0
        return Calendar.current.date(from: defaultTime) ?? Date()
    }

    @State private var wakeUp = defaultWakeUpTime
    @State private var sleepAmount = 8.0
    @State private var coffeeAmount = 0 {
        didSet {
            calculateSleepTime()
        }
    }

    @State private var showTime : String = " "

    func calculateSleepTime() {**CONTENT**}

    var body: some View {
        NavigationView {
                VStack {
                    Spacer(minLength: 20)

                    Text("Your optimum sleep time is \(showTime)")

                    Spacer(minLength: 10)

                    Section {
                    Text("When do you want to wake up?")
                        .font(.headline)
                        DatePicker("Please choose a time", selection: $wakeUp, displayedComponents: .hourAndMinute)
                        .labelsHidden()
                        .datePickerStyle(WheelDatePickerStyle())
                    }

                Spacer()

                    Form {
                        Text("How many hours would you like to sleep?")
                            .font(.headline)
                        Stepper(value: $sleepAmount, in: 4...12, step: 0.25) {
                            Text("\(sleepAmount, specifier: "%g" ) hours")
                        }

                    }

                Spacer()

                    Section {
                        Text("How many cups of coffee do you drink?")
                            .font(.headline)

                        Picker("Coffee Selector", selection: $coffeeAmount) {
                            ForEach (1..<21) {
                                Text("\($0) " + "Cup")
                            }
                        }
                        .labelsHidden()
                    }
                }
                .navigationBarTitle(Text("BetterSleep"))
                .onAppear(perform: calculateSleepTime)
        }
    }
}

Answer 1

我将使用viewModel并使用订阅来跟踪值并计算睡眠时间。

将顶部的ContentView更改为此

struct ContentView: View {
    @ObservedObject var viewModel = ViewModel()

现在在所有变量之前加上viewModel.

创建一个新的.swift文件，我只是将其命名为ViewModel，但是您不必这样做。

import Combine

final class ViewModel: ObservableObject {
    @Published private(set) var bedTime: String = ""
    @Published var wakeUp: Date = Date()
    @Published var sleepAmount: Double = 8.0
    @Published var coffeeAmount = 0
    private var cancellables = Set<AnyCancellable>()

    init() {
        $wakeUp
            .receive(on: RunLoop.main)
            .sink { [weak self] _ in
                self?.calculateSleepTime()
        }.store(in: &cancellables)

        $sleepAmount
            .receive(on: RunLoop.main)
            .sink { [weak self] _ in
                self?.calculateSleepTime()
        }.store(in: &cancellables)

        $coffeeAmount
            .receive(on: RunLoop.main)
            .sink { [weak self] _ in
                self?.calculateSleepTime()
        }.store(in: &cancellables)
}

    private func calculateSleepTime() {
        // Your Logic
        self.bedTime = 
    }
}

现在，只要其中一个值发生更改，建议的就寝时间就会更新。请记住，从0开始，将其添加到coffeeAmount中。

通过更改变量更新视图

1 个答案: